1. Field of the Invention
The present invention relates to a polyphenylene sulfide (hereafter, referred to as PPS) resin composition for use in molding which can reduce the occurrence of corrosion in metal molds used during molding operations as well as the occurrence of corrosion in metal portions of assembled parts using molded articles produced from such resin composition.
2. Prior Art
As is well known, PPS resins have a very high heat resistance, chemical resistance, electric characteristics and flame resistance and in addition they exhibit an excellent mechanical strength, rigidity and dimensional stability when reinforced with a reinforcing filler or the like. Therefore, they are used widely in various molding applications such as production of electric and electronic parts, parts of automobiles and even parts of machines.
However, PPS resins cause problems in that they generate gases which are corrosive to metals at high temperatures or in a molten state, with the result that metal molds and molding machines would be corroded during the molding operation, or when molded articles are aged at a temperature not lower than 100.degree. C. and not higher than the melting point of the resin, metal portions of assembled parts including the molded articles or inserted metal parts would be corroded. Various problems can result, for instance, relay bases in which PPS resin is used would often suffer the occurrence of corrosion on its metal contact, resulting in poor contact, and in other occasions, adhesion of soldering in inserted metal portions decreases due to its corrosion.
Conventional proposals for overcoming the above-described problems include a method in which an alkali metal hydroxide or carbonate is added as described in U.S. Pat. No. 4,017,450, a method in which a hydroxide, oxide or aromatic carboxylic acid salt of a metal belonging to the group IIA of the periodic table as described in Japanese Patent Publication (Kokai) No. Sho 62-109850, and the like.
However, none of the conventional proposals were successful in giving sufficient effects. The compounds used in either methods are soluble in water or hygroscopic if insoluble in water, resulting in that the addition of the above-described compounds decreases the water resistance of the resulting resin composition, and accordingly, when the resin composition is used as an insulation material as reinforced with glass fiber or the like, the insulation characteristics of the material under highly hygroscopic conditions decreases to a greater extent.
Also, a method is known in which hydrotalcite is added to PPS resin in order to reduce metal corrosiveness as described in U.S. Pat. No. 4,529,769. However, this method is inferior in the effect of reducing the metal corrosiveness as compared with the method in which an alkali metal hydroxide or carbonate is added, although its water resistance and insulation characteristics do not decrease so much.